The present invention relates to a method and apparatus for monitoring the yarn tension of a continuously advancing yarn, such as at each of the operating positions of a false twist crimping machine.
U.S. Pat. No. 4,720,702 to Martens discloses a method for continuously monitoring the yarn tension at each of a plurality of yarn processing stations, and which involves continuously determining the mean value of the monitored tension at each station, and continuously determining the differential between the monitored value and the mean value. An alarm signal is generated whenever the mean value leaves a predetermined tolerance range, and also whenever the differential value leaves a second predetermined tolerance range.
In the above described method, the upper limiting value of a mean value and the lower limiting value of a mean value are set so far apart from each other for the control of the entire false twist texturing machine, as to ensure that the mean values of all working positions are within these centrally set values. Consequently, the mean value of the individual positions is able to fluctuate within a relatively wide range, which adversely affects the accuracy of the method.
It is accordingly the object of the present invention to provide a method and apparatus for monitoring the yarn tension at each of a plurality of yarn processing stations of a yarn processing machine, and wherein it is possible to respond to relatively small fluctuations of the mean value at each position.